It has long been known that nitriles can be reduced to give amines. Typically a mixture of primary, secondary and tertiary amines are produced, and a common goal is to devise a process by which the result is a yield high in only one of the possible products; that is, has high selectivity to a particular product. The reaction is understood to proceed in two steps, and often the process is a two step process, usually using a different catalyst for the two steps. Frequently, the reaction is run as a batch reaction inasmuch as good selectivities have been difficult to achieve using continuous processes.
Particularly useful products from the reaction are the secondary amines. They have found such widespread uses as textile additives, disinfectants, antistatic agents, and organophilic ammonium bentonites. Especially useful are the unsaturated long-chain aliphatic secondary amines since the quaternary ammonium salts thereof can provide softness and antistaticity to various fabrics and hair, and can also be used as a softener for providing water absorbancy and handling ease to treated fabrics. The secondary amine ditallowamine is useful in the preparation of surfactants, but has never been continuously prepared in high selectivity from tallow nitrile. Tallow nitrile has sixteen to eighteen carbon atoms (C.sub.16 to C.sub.18).
Of particular interest is British Patent 1,180,972 (equivalent to Oberrauch, Hans, et al. "Secondary Fatty Amines", Chemical Abstracts, 70:11108n, West German Patent 1,280,243, 1969, p. 221) which teaches that aliphatic, saturated and unsaturated secondary fatty amines can be prepared by hydrogenation of the corresponding fatty acid nitrile by passing the nitrile at 140.degree.-200.degree. C. and 30-200 atm. of hydrogen together with water over a solid catalyst consisting of 20% copper, 0.8% chromium and 1% alkali metal with a wide-poured silica gel having a specific area of 250-350 m..sup.3 /g as the support. See also British Patent 1,323,351 (equivalent to West German Auslegeschrift 1,941,290) which describes a process for making aliphatic saturated secondary amines from nitriles having 8 to 22 carbon atoms per molecule, where in a first step the starting product is hydrogenated to yield a mixture of saturated amines, and in a second step, this mixture is continuously desaminated (i.e., ammonia is split off) optionally with the addition of hydrogen, where each step is carried out in the presence of a fixed bed hydrogenation catalyst. The first step is conducted at a hydrogen pressure of from 100 to 300 atmospheres gauge and at a temperature in the range of from 100.degree. to 200.degree. C., while the second step is conducted at a pressure from 0 to 50 atmospheres and at a temperature in the range from 120.degree. to 220.degree. C. The catalysts used are a cobalt catalyst in the first step and then a copper catalyst; or alternatively a nickel catalyst in the first reaction and a cobalt catalyst in the second.
Tertiary monomethylamines having long chain alkyl groups are advantageously prepared from unsaturated aliphatic nitriles under a low pressure at a high yield by a three step process according to U.S. Pat. No. 4,248,801. The first step involves reducing nitriles with hydrogen in the presence of a nickel hydrogenation catalyst at 200.degree. C. and under a hydrogen pressure of 0 through 10 kg/cm.sup.2 G, while the formed ammonia is removed.
Of lesser importance is the following group of publications, which includes U.S. Pat. No. 2,781,399, (equivalent to British Pat. 759,291) that teaches production of secondary aliphatic hydrocarbon amines via a batch reaction using a nickel hydrogenation catalyst. A similar process is described in U.S. Pat. No. 2,811,556, except that a copper oxide/chromium oxide catalyst is used.
Tomidokoro, S., et al., "Preparation of Long-Chain Secondary Amines by Reduction of Nitriles", Chemical Abstracts, 106:175777t, Japan Tokkyo Koho JP 62 00,901, 1987, p. 671, teaches the preparation of long-chain secondary amines by the reduction of aliphatic nitriles having 8 to 22 carbon atoms over nickel catalysts at 0-6 kg/cm.sup.2 gauge and 200.degree. to 230.degree. C. while removing more that 85% formed NH.sub.3. Thus, 250 g. of tallow nitrile was reduced over 0.5 g. Ni catalyst at 200.degree.-300.degree. C. and 5 kg/cm.sup.2 while removing 93% formed NH.sub.3 to give 240 g. of a mixture of primary (3.1%), secondary (91.1%) and tertiary amine (4.3%) amines.
European patent 0 021 162 B1 teaches the production of alkylamines with 12 to 22 carbon atoms by hydrogenating corresponding fatty nitriles in the presence of a nickel or cobalt catalyst. The hydrogen gas reactant is recirculated after removal of ammonia. The new feature is that throughout the reaction the water content of the circulating gas is adjusted to not above 5 g. per cubic meter, under practically zero-pressure conditions, before recycle. Additionally, a process for selectively preparing an unsaturated long-chain aliphatic secondary amine at a high yield involving reducing an unsaturated aliphatic nitrile having 8 to 22 carbon atoms or a nitrile mixture containing said nitrile with hydrogen in the presence of a nickel hydrogenation catalyst and a carboxylic acid amide at a reaction temperature of 160.degree. to 200.degree. C. is described in European Patent Application 0232097 A2.
A process for the selective production of aliphatic secondary amines from C.sub.8-22 primary amines using dehydrogenation/hydrogenation catalysts is briefly mentioned in the English abstract to East German Application 133,229-A. In a first stage, the primary amine is dehydrogenated at normal pressure and at 170.degree. to 260.degree. C., by treatment with a inert gas (N.sub.2) in an amount of 5 to 150 l/mol./h., for 30 to 60 minutes until a degree of conversion of the starting material of 85-98% is achieved. The resulting dehydrogenated product is then reacted with hydrogen at 100.degree. to 140.degree. C. and 0 to 50 atmospheres for 10 to 30 minutes to form the secondary amine. The nature of the catalyst was not mentioned in the abstract.
There remains a need for a continuous process for producing fatty secondary amines simply, and in high selectivities. Ideally, such a process would only use one catalyst.